CA2088626C - Load-control circuit for a mains-powered asynchronous single-phase capacitor motor - Google Patents

Load-control circuit for a mains-powered asynchronous single-phase capacitor motor

Info

Publication number
CA2088626C
CA2088626C CA002088626A CA2088626A CA2088626C CA 2088626 C CA2088626 C CA 2088626C CA 002088626 A CA002088626 A CA 002088626A CA 2088626 A CA2088626 A CA 2088626A CA 2088626 C CA2088626 C CA 2088626C
Authority
CA
Canada
Prior art keywords
load
control circuit
motor
voltage
capacitor
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
CA002088626A
Other languages
French (fr)
Other versions
CA2088626A1 (en
Inventor
Daniel Fluckiger
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Ascom Hasler Mailing Systems AG
Original Assignee
Ascom Hasler Mailing Systems AG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ascom Hasler Mailing Systems AG filed Critical Ascom Hasler Mailing Systems AG
Publication of CA2088626A1 publication Critical patent/CA2088626A1/en
Application granted granted Critical
Publication of CA2088626C publication Critical patent/CA2088626C/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

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Classifications

    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02PCONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P25/00Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details
    • H02P25/02Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the kind of motor
    • H02P25/04Single phase motors, e.g. capacitor motors

Abstract

Disclosed is a circuit for controlling the load of an asynchronous motor (11), the circuit comprising two capacitors (19, 20), one of which (20) can be connected, by means of a switch (70), in parallel with the other (19).
Control is provided by a current sensor (30) and a voltage sensor (40), whose signals (S1, S2) are compared by a comparator (25). Depending on the relative size of the signals (S1, S2) a switch control unit (60) with relaxation hysteresis characteristics switches the switch (70) on or off. The circuit is simple, operates independently of the mains voltage (U) being used and its switch point can be adjusted by means of the current sensor (30).

Description

LOAD-CONTROL CIRCUIT FOR A MAINS-POWERED
ASYNCHRONOUS SINGLE-PHASE CAPACITOR MOTOR
The invention relates to load-control circuit for a mains-operated single-phase asynchronous capacitor motor corresponding to the preamble of claim 1. The invention relates further to the use of such a circuit in a postage metering machine.
Asynchronous capacitor motors, which are operated at the general single-phase mains (for example 220 V, 50Hz) are known in general and widespread. They are economical, sturdy, and operate without service requirements. In addi-tion to their positive properties, however, they are also associated with disadvantages. The asynchronous capacitor motors have a poor efficiency, which is in general below 50%. Thereby a relatively large power dissipation is always generated, where the power dissipation can heat the motor windings up to critical temperatures of above 100~C.
This substantial power dissipation is also present during idling of the motor.
It is further known that asynchronous capacitor motors furnish only a relatively small starting torque dur-ing the starting from a standstill. For improving of this property an additional capacitor can be connected to the motor capacitor for starting.
A postage metering machine is known from Hasler Review, Vol. 11, 1978, No.l, pages 2-7, which postage meter-ing machine includes an asynchronous capacitor motor as a drive. This motor runs in the substantially idling state after the switching on of the machine, wherein the motor drives the pull-in rollers for the letters to be metered. As soon as the letter is to be metered, the print rotor of the machine is coupled to the motor and accelerated through a coupler. The mechanical load of the capacitor motor increases substantially for a short time during this proce-dure.
The mode of operation of ~he capacitor motor i5 thus such that the capacitor motor is loaded pred~min~ntly only very little in order to be loaded substantially more over a short time period. The strength o~ the load depends in this case also on the kind of the letters which have to be metered, in particular on the thickness of these letters, where the thickness can vary between less than 1 mm and about 8 mm.

-- 3 ~

The construction of the capacitor motor in this case is directed to the load peaks whereby, in case of a weak load, there result relatively unfavorable operating condi-tions and where, based on the unfavorable operating condi-tions, the complete postage metering machine is subjected to a substantial thermal load.
It is an object of the invention to furnish a gen-eral drive motor for a postage metering machine with its specific kind of motor load, where the drive motor generates substantially less heat than up to now while maintaining the general costs at the same level.
The solution of this object is furnished by the characterizing part of the independent claims. The dependent claims provide specific embodiments of the invention.
The invention is described in the following in more detail by way of the e~amples in two figures. There is shown in:
Fig. 1 - schematic diagram of a load-control cir-cuit.
Fig. 2 - detailed switching diagram of the load-control circuit.

20886~6 Fig. 1 shows the schematic diagram of a load-control circuit for a mains~operated single-phase asynchronous capa-citor motor 11. This motor 11 is constructed for example with four poles. The main windings of the motor are con-nected through the connections 13, 14 as well as 15 to a single-phase alternating-current mains of the standard 220 V, S0 Hzb, or 110 V, 60 Hz, for example through a mains plug 18. A first capacitor 19 is connected to a shunt winding of the motor 11, and this shunt winding is connected to the connection 15 with alternating current through which capa-citor 19.
The arrangement described so far corresponds to a generally known capacitor motor, wherein the windings of the motor 11 and the capacity value of the first capacitor 19 are tuned in such a way to each other that optimum situa-tions result in connection with the substantially unloaded running of the motor 11, i.e. in particular a lowest pos-sible power dissipation.
There is now provided a second capacitor 20, where the second capacitor 20 can be connected to the motor by means of a switch arrangement 70 in parallel to the first capacitor 19. The capacitance value of the two capacitors 19, 20 together is thereby selected such that the motor 11 .~, . ~: -~ ' :
2~8626 can handle substantial load peaks without problems, whereinthe load peaks, however, are in each case extending only over a relatively short time.
The load-control circuit comprises further a cur-rent sensor 30, a voltage sensor 40, a comparator 25 with a relaxation hysteresis and a switch control unit 60.
The current sensor 30 detects continuously the cur-rent strength in the connection line 14, where the current strength in the line 14 corresponds to the current strength in the main winding of the motor ll. The current sensor 30 further delivers at its output 36 a first direct current signal Sl, which direct current signal Sl is proportional to the current i. The voltage sensor 40, in parallel to the current sensor 30, detects continuously the mains voltage U
and delivers at its output 39 a second direct current signal S2, where the second direct current signal S2 is propor-tional to the voltage U. The two direct current signals Sl, S2 are continuously compared in the comparator 25. As soon as the first signal Sl becomes larger than the second signal S2, the comparator 25 flips out of its rest position into its working position. If the second signal S2 becomes again larger than the first signal Sl then the comparator 25 flips back into its rest position. The relaxation hysteresis is 2088~26 generated thereby based on two slightly different relaxation values of the comparator 25 and prevents a possible oscilla-tion of the comparator 25 in case the two signals Sl, S2 have equal values.
The switch arrangement 70 is preferably produced as a semiconductor switch, for example as a triac. The switch control 60 is connected in series to the semiconductor switch, where the switch control 60 prevents a damaging of the switch. In particular, the switch control 60 makes provisions that the semiconductor switch is only switched on in case of a zero passage of the voltage.
Fig. 2 shows the circuit diagram of a preferred embodiment of the load-control circuit. The current sensor 30 comprises a low resistance measuring resistor 31, which is inserted into the connection line 14. The voltage drop at this resistor 31 is proportional to the main winding current of the motor 11, the voltage drop is rectified by a diode 32 and is smoothed by a the capacitor 33, where a high-resistance discharge resistor 34 is switched parallel to the capacitor 33. The generated sensor voltage is buffered in an operational amplifier 35 and is delivered as first direct voltage signal Sl by the connection line 36 to the plus input of the comparator 25. The diod~ 32 and the capacitor :' 33 form in this case, generally considered, a very simple rectifier and filtering device.
The voltage sensor 40 comprises a voltage divider comprising two resistors 41, 42, where the voltage divider is connected to the connection lines 13, 15, and where a diode rectifier 44 and a smoothing capacitor 45 with parallel-connected discharge resistor 46 is connected to the tap 43 of the voltage divider for the formation of a second direct current signal S2.
The comparator 25 with relaxation hysteresis is formed by an operational amplifier, where the operational amplifier feeds back through a resistor 53 from its output 52 to its plus input (+) and is connected through a further resistor 57 to the output 36 of the current sensor 30. The recited relaxation hysteresis is generated and the relaxa-tion values are set based on this wiring circuit. The output 52 of the comparator 25 controls a light-emitting diode (LED) 55 with a transistor 54, where the light-emitting diode 55 is part of an optical coupler.
The optical coupler separates the relaxation circuit 50 and the switch control unit 60 relative to voltage. The switch control unit 60 has the purpose to switch the switch of the switch arrangement 70 in each case then, when the : ~ ' .

~ 2o88626 phototransistor 61 of the optical coupler responds and when the respective next zero passage of the voltage applied to the switch occurs. For this purpose, a zero-voltage detector circuit is connected following to the phototransistor 61, such as the zero-voltage detector circuit described in "Thyristors & Triac Application Manual 1989" of the corpo-ration SGS-Thomson, pages 57 and ff.
The switch arrangement 70 comprises a triac 71 as a switch, where the triac 71 is switched on by the switch con-trol unit 60, as described above, in case of a zero passage of the a~ternating current voltage. For safety purposes, a resistor 72 is connected in series with the triac 71, which resistor 72 can limit nevertheless possibly occurring cur-rent peaks. A voltage-dependent resistor (VDR) 73 is con-nected parallel to the resistor 72 and to the triac 71, where the voltage-dependent resistor 73 limits possibly occurring overvoltages during interruptions of the triac tl.
The load-control circuit forms together with the motor 11 an economical solution of the problem recited. The load control circuit provides for a substantial reduction of the conventionally usual power dissipation without neces-sitating decisive constructive steps for the postage meter-ing machine. The load-control circuit offers at all times a _ g _ 2088~26 safe distinction between differing work loads of the motor 11, independent of overvoltages or undervoltages at the mains plug 18, based on a simultaneous measurement of the motor current i and of the mains voltage U. The differing work loads can thereby be, for example "Idling of the Postage Metering Machine~' and "Driving of the Print Rotor".
However, it is preferred to provide the distinction between the states "Idling" and "Work Load Caused by a Thick Envelope". The latter load can of course occur only in case of a rotation of the print rotor.
The load-control circuit can be varied relative to the exact circuit of Fig. 2 in a multitude of ways. For example, other semiconductor elements can be employed instead of the triac 71, the current sensor 30 can be of a more elaborate construction, etc. without that the invention as such would be touched by such measures.

. . ~

Claims (5)

1. Load-control circuit for an asynchronous motor (11), where the asynchronous motor is operated at a single-phase mains with the aid of a first capacitor (19), wherein a second capacitor (20) is furnished, which can be connected in parallel to the first capacitor (19) by a switch (70), characterized by a current sensor (30) for the continuously detecting the motor current (i) through the main winding of the motor (11) and for delivering of a first direct current signal (S1) proportional to this current (i), by a voltage sensor (40) for continuously detecting the mains voltage (U) and for delivering a second direct current signal (S2) proportional to the mains voltage, by a comparator (25) with relaxation hysteresis for continuously comparing the first direct current signal (S1) and the second direct current signal (S2) and for delivering in each case a switching signal at the switch (70), as long as the first signal (S1) is larger than the second signal (S2).
2. Load-control circuit according to claim 1, characterized in that the current sensor (30) is a resistor (31) and that the voltage sensor (40) is a voltage divider (41, 42), in each case with a series-connected rectifier and filtering device (32-34; 44-46).
3. Load-control circuit according to claim 1, characterized in that a switch control unit (60) is furnished which, as soon as a switching signal of the comparator (25) occurs, switches on the comparator at the next following zero passage of the voltage at the switch (70).
4. Load control circuit according to claim 3, characterized in that an optical coupler (55, 61) is furnished, where the optical coupler (55, 61) is inserted between the comparator (25) and the switching control unit (60) for purposes of voltage separation.
5. Use of a load-control circuit according to claim 1 in a postage metering machine, which postage metering machine includes an asynchronous motor (11), wherein the asynchronous motor (11) is continuously operated at a single-phase mains and, wherein a print rotor can be coupled to the asynchronous motor (11), wherein the print rotor is controlled and put into rotation by a coupling, characterized in that the load-control circuit is set such that the load control circuit switches the second capacitor (20) parallel to the firs-t capacitor (19) upon a rotation of the print rotor and only in case of a comparatively large load of the motor (11).
CA002088626A 1991-06-07 1992-06-04 Load-control circuit for a mains-powered asynchronous single-phase capacitor motor Expired - Fee Related CA2088626C (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CH01697/91-7 1991-06-07
CH169791 1991-06-07

Publications (2)

Publication Number Publication Date
CA2088626A1 CA2088626A1 (en) 1992-12-08
CA2088626C true CA2088626C (en) 1998-01-06

Family

ID=4216485

Family Applications (1)

Application Number Title Priority Date Filing Date
CA002088626A Expired - Fee Related CA2088626C (en) 1991-06-07 1992-06-04 Load-control circuit for a mains-powered asynchronous single-phase capacitor motor

Country Status (6)

Country Link
US (1) US5359273A (en)
EP (1) EP0542955B1 (en)
AT (1) ATE130980T1 (en)
CA (1) CA2088626C (en)
DE (1) DE59204500D1 (en)
WO (1) WO1992022126A1 (en)

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US5719381A (en) * 1995-04-14 1998-02-17 Ascom Hasler Mailing Systems Ag Postage meter with hollow rotor axle
US5654614A (en) * 1995-04-14 1997-08-05 Ascom Hasler Mailing Systems Ag Single-motor setting and printing postage meter
US5668973A (en) * 1995-04-14 1997-09-16 Ascom Hasler Mailing Systems Ag Protection system for critical memory information
US5746133A (en) * 1995-05-22 1998-05-05 Ascom Hasler Mailing Systems Ag Postage meter with rotor movement and die cover sensor
US5689098A (en) * 1995-05-26 1997-11-18 Ascom Hasler Mailing Systems Ag Postage meter with improved postal lock
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US7243174B2 (en) * 2003-06-24 2007-07-10 Emerson Electric Co. System and method for communicating with an appliance through an optical interface using a control panel indicator
US7280769B2 (en) * 2003-07-28 2007-10-09 Emerson Electric Co. Method and apparatus for operating an optical receiver for low intensity optical communication in a high speed mode
US7091932B2 (en) * 2003-07-28 2006-08-15 Emerson Electric Co. Method and apparatus for independent control of low intensity indicators used for optical communication in an appliance
US7321732B2 (en) * 2003-07-28 2008-01-22 Emerson Electric Co. Method and apparatus for improving noise immunity for low intensity optical communication
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US7095333B2 (en) * 2003-09-18 2006-08-22 Emerson Electric Company Method and apparatus for enabling optical communication through low intensity indicators in an appliance that uses a vacuum fluorescent display
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Also Published As

Publication number Publication date
CA2088626A1 (en) 1992-12-08
DE59204500D1 (en) 1996-01-11
US5359273A (en) 1994-10-25
WO1992022126A1 (en) 1992-12-10
EP0542955B1 (en) 1995-11-29
EP0542955A1 (en) 1993-05-26
ATE130980T1 (en) 1995-12-15

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